Thermoplastic and thermosetting polymers are used to form a wide variety of structures for which properties such as abrasion resistance, optical clarity (i.e., good light transmittance) and/or the like, are desired characteristics. Examples of such structures include camera lenses, eyeglass lenses, binocular lenses, retroreflective sheeting, automobile windows, building windows, train windows, boat windows, aircraft windows, vehicle headlamps and taillights, display cases, eyeglasses, watercraft hulls, road pavement markings, overhead projectors, stereo cabinet doors, stereo covers, furniture, bus station plastic, television screens, computer screens, watch covers, instrument gauge covers, bakeware, optical and magneto-optical recording disks, and the like. Examples of polymer materials used to form these structures include thermosetting or thermoplastic polycarbonate, poly(meth)acrylate, polyurethane, polyester, polyamide, polyimide, phenoxy, phenolic resin, cellulosic resin, polystyrene, styrene copolymer, epoxy, and the like.
Many of these thermoplastic and thermosetting polymers have excellent rigidity, dimensional stability, transparency, and impact resistance, but unfortunately have poor abrasion resistance. Consequently, structures formed from these materials are susceptible to scratches, abrasion, and similar damage.
To protect these structures from physical damage, a tough, abrasion resistant "hardcoat" layer may be coated onto the structure. Many previously known hardcoat layers incorporate a binder matrix formed from free-radically curable prepolymers such as (meth)acrylate functional monomers. Such hardcoat compositions have been described, for example, in Japanese patent publication JP 02-260145, U.S. Pat. Nos. 5,541,049, and 5,176,943. One particularly excellent hardcoat composition is described in WO 96/36669 A1. This publication describes a hardcoat formed from a "ceramer" used, in one application, to protect the surfaces of retroreflective sheeting from abrasion. As defined in this publication, a ceramer is a composition having inorganic oxide particles, e.g., silica, of nanometer dimensions dispersed in a binder matrix.
Many ceramers are derived from aqueous sols of inorganic oxide particles according to a process in which a free-radically curable binder precursor (e.g., one or more different free-radically curable monomers, oligomers, and/or polymers) and other optional ingredients (such as surface treatment agents that interact with the inorganic oxide particles, surfactants, antistatic agents, leveling agents, initiators, stabilizers, sensitizers, antioxidants, crosslinking agents, crosslinking catalysts, and the like) are blended into the aqueous sol. The resultant ceramer composition may then be dried to remove substantially all of the water. The drying step may also be referred to as "stripping". An organic solvent may then be added, if desired, in amounts effective to provide the ceramer composition with viscosity characteristics suitable for coating the ceramer composition onto the desired substrate. After coating, the ceramer composition can be dried to remove substantially all of the solvent and then exposed to a suitable source of energy to cure the free-radically curable binder precursor, thereby providing the desired, abrasion resistant hardcoat layer on the substrate.
Although such ceramer compositions, upon curing, generally provide at least some level of abrasion resistance to a substrate, they generally do not provide appreciable stain resistance or oil and/or water repellency. As a result, substrates comprising a cured ceramer composite are susceptible to staining due to prolonged contact with oil, water or other stain causing agents. Such staining impairs the optical clarity and appearance of the substrate. It is therefore desirable to incorporate agents into ceramer compositions that will provide the ceramer composition, upon, curing, with stain, oil and/or water resistance, while still maintaining the desired hardness and abrasion resistance characteristics of the resultant, cured ceramer composite.
Fluorochemicals tend to form compositions with low surface energy, and compositions with a low surface energy generally tend to show better stain, oil and water repellency than compositions with a higher surface energy. Thus, the incorporation of a fluorochemical into a ceramer composition would be desirable in order to enhance the ability of a cured ceramer composite to repel oil and/or water, and to resist staining.
Unfortunately, however, the incorporation of fluorochemicals into a ceramer composition is extremely difficult. Because fluorochemicals are both hydrophobic (incompatible with water) and oleophobic (incompatible with nonaqueous organic substances), the incorporation of a fluorochemical into a ceramer composition, which is hydrophilic, often results in phase separation between the fluorochemical and other ingredients of the ceramer composition. Colloid flocculation may also result. This undesirable phase separation and/or colloid flocculation can result not only when the ingredients are mixed together, but also during the stripping process, i.e., when water is removed from the blended ceramer composition. Finally, not only can fluorochemicals be incompatible with the colloidal inorganic oxide component of ceramer compositions, but such materials also would be expected to adversely affect the hardness and abrasion resistance characteristics of a resultant cured ceramer composite into which such fluorochemicals are incorporated.
It would thus be desirable to provide a ceramer composite that exhibits both the desired hardness and abrasion resistance characteristics, while also exhibiting stain, oil and/or water repellency. It would further be desirable to utilize fluorochemicals to provide the desired stain, oil and/or water repellency, while avoiding compatibility and hardness problems generally associated with the incorporation of fluorochemicals into ceramer compositions.